Storms off the Southern Ocean are driving more rainfall—and the ripple effects could reach every corner of the globe.
If you ever visit Macquarie Island—a narrow, wind-battered ridge about halfway between Tasmania and Antarctica—the wildlife is immediately striking. Elephant seals blanket the dark beaches. King penguins march up mossy slopes. Albatrosses wheel over vast, treeless highlands.
But a closer look reveals change beneath the surface. Slopes are turning boggier, and iconic megaherbs like Pleurophyllum and Stilbocarpa are retreating. For years, scientists suspected rising rainfall as the culprit. Our latest study, published in Weather and Climate Dynamics, confirms this link and shows the phenomenon extends far beyond this remote UNESCO World Heritage site.
A major but underappreciated climate driver
The Southern Ocean plays a pivotal role in shaping global climate.
It absorbs a large share of the excess heat trapped by greenhouse gases and a substantial portion of human-emitted carbon dioxide. Storm activity there also influences weather patterns across Australia, New Zealand, and the broader world. Yet it remains one of the least observed regions on Earth.
With virtually no landmasses, few weather stations, and near-constant cloud cover, satellite data and climate models struggle to capture real conditions in this ocean belt.
That makes Macquarie Island’s climate record—from the Bureau of Meteorology and the Australian Antarctic Division—especially valuable. It provides one of the rare long-running, ground-truth records for the Southern Ocean, documenting daily rainfall and meteorology for more than seven decades and commonly used to validate satellite products and climate simulations.
Rising rainfall, on the record
Earlier research found that rainfall on Macquarie Island had risen sharply in recent decades, and ecologists documented how waterlogging harmed native vegetation. However, the mechanistic link—how the island’s weather patterns were shifting and how observed data aligned with historical climate reconstructions—had not been fully explored.
To address this gap, the team analyzed 45 years of daily rainfall observations (1979–2023) and compared them with ERA5, a widely used reanalysis of past weather. The goal was to uncover the meteorological drivers behind the rainfall increase—whether more storms were forming or existing storms were delivering more rain. Each day was categorized into five synoptic regimes based on pressure, humidity, winds, and temperature, including low-pressure systems, cold-air outbreaks, and warm-air advection (the warm air moving poleward ahead of cold fronts).
Storms are delivering more rain
The results show that Macquarie Island’s annual rainfall has risen by about 28% since 1979, roughly 260 millimeters per year. By contrast, ERA5 indicates only an 8% increase, missing much of the actual change.
The well-documented shift of the storm track toward Antarctica has been in place for some time, and this study demonstrates how that broader shift is shaping the island’s weather today.
Crucially, the increase in rainfall is not simply the result of one wet regime displacing another. Warm-air advection has largely replaced low-pressure conditions, but the key finding is that storms now deliver more rain when they occur.
Why this matters beyond a single island
If the rainfall intensification seen at Macquarie Island mirrors conditions across the Southern Ocean storm belt—as several lines of evidence suggest—the implications are substantial.
A wetter storm track means more freshwater entering the upper ocean. This addition strengthens vertical layering and reduces mixing, which can alter ocean currents.
Estimating from 2023 data, this extra precipitation amounts to about 2,300 gigatonnes of additional freshwater per year across the high-latitude Southern Ocean—an amount an order of magnitude larger than recent Antarctic meltwater contributions. And the trend is growing.
Higher rainfall also affects surface salinity, influencing nutrient and carbon movement. This could modify the productivity and chemistry of the Southern Ocean, a crucial global carbon sink, in ways that are still not fully understood.
To balance the increased rainfall, evaporation must rise as well, which cools the ocean. Evaporation is the primary cooling mechanism for the cloudy Southern Ocean.
The analysis suggests the Southern Ocean may be cooling itself by 10–15% more than in 1979 simply because evaporative cooling scales with the extra rainfall across the wider ocean.
In effect, the Southern Ocean could be experiencing more intense “sweating” in response to climate change.
What’s next
Macquarie Island represents a tiny fragment of Earth’s stormiest ocean, yet its long-running rainfall record points to a faster, more dramatic shift in the Southern Ocean—arguably the engine room of global heat and carbon uptake—than previously thought.
The next step is to determine how far this signal extends along the storm track and what it means for the broader climate system that people depend on.
The authors acknowledge Andrew Prata, Yi Huang, Ariaan Purish, and Peter May for their contributions to this research and the article.
